The technic of intermittent mandatory ventilation assures automatically a fraction of ventilatory cycles on a patient who has a spontaneous ventilation. This mechanism used in medical and surgical resuscitation, on twenty one patients of different age-group, has allowed the objectivation of the following elements: - the clinical and the analysis of gaz results are found to be satisfactory at the end of the first hour; - one the contrary from then on, the results tend to differ on the basis of the periods of misadaptation which are more or less long and frequent. Looking after such a ventilatory devise demands as much intensing attention as that of any other artificial ventilation.